1. Field of the Invention
This invention is related to electrosurgical systems and more particularly to a solid state electrosurgical generator system suitable for generating cutting and fulgurating electrosurgical currents.
2. Discussion of the Prior Art
Electrosurgical systems have been used for surgical procedures since the early part of the twentieth century with only minor changes until the past several years. The unchanged basic principle lies in the fact that a radio-frequency, or RF, electrical current which oscillates in the range of 0.4 to 2.5 megahertz can be used to cut or sear flesh without disturbing the nerve functions of the patient or operator.
The RF current is generated by a generator in an electrosurgical system and fed to an active electrode which generates heat at the operating site when the active electrode is placed in contact with the patient. The circuit is completed through a portion of the patient to an indifferent or return electrode which is placed in contact with the patient to supply a return path for the current to the electrosurgical generator.
Electrosurgery is considered better than the conventional scalpel for operations involving tissues with oozing capillary beds, particularly in organs such as liver, spleen, thyroid and lung, because it can provide either simultaneous or sequential cutting and coagulation or hemostasis thereby providing faster and neater sectioning of these organs. Because of the increased operating speed in the hand of a skilled surgeon, electrosurgery is a preferred technique for organ transplants and for long involved operations.
The first application of RF current for electrosurgery in the early 1900's used a spark gap or Tesla coil to generate a "fulguration" current. The fulguration current involved a series of rapidly damped RF waves having an initial high voltage amplitude. While not useful for cutting flesh, the fulguration effect charred surrounding flesh, producing a coagulation or hemostasis effect over quite a broad surface.
Electrosurgical systems introduced later in the early part of this century used vacuum tubes to produce a RF current of steady or undamped amplitude for use in a cutting mode, hereinafter referred to as a "cut" current. Since the steady Rf output of the vacuum tubes had much lower peak voltage output, and much higher average power, these units were not useful for producing coagulation. For many years, the practical use of electrosurgery required the use of large bulky generators which combined the features of both a spark-gap RF generator and a vacuum tube type RF generator so that both a fulguration current and a cut current could be provided to the active electrode as needed.
Within the past several years many solid state electrosurgical systems have been developed. These contain compact RF generators of much improved reliability, efficiency and safety. These systems usually provide at least two separate and distinct RF current waveforms to the active electrode, to wit: a continuous undamped relatively low voltage cut mode current similar to that of the outdated vacuum tube generator and either a damped or interupted (or damped and interupted) likewise low voltage current for use in coagulating mode, hereinafter referred to as a "coagulate" current.
Most of these solid state electrosurgical systems, such as those described in U.S. Pat. No. 3,675,655 to Sittner, and U.S. Pat. No. 3,699,967 to Anderson, are quite versatile, providing in addition to both a cutting mode and a coagulation mode, a combined cutting and coagulation mode wherein a "blend" current is provided. In spite of such versatility the new solid state electrosurgery systems have not been widely accepted because they do not provide a fulguration current as do the old bulky electrosurgical systems that the surgeon is familiar with. The coagulate current although somewhat similar to the fulguration current of the outdated spark gap units is at a lower peak voltage and hence the effect is different. Production of heat, either at the arc or in adjacent tissue, is a function of both current density and duration. The fulguration effect produced by the old spark-gap generators produced a sparking from the active electrode, while adjacent to but not in contact with the flesh that caused desication or hemostasis over a fairly wide area of adjacent tissue. Modern solid state electrosurgical systems, when used in the coagulating mode, produce a highly localized hemostasis effect, such that the active electrode must be separately touched to almost all of the many individual "bleeders". This is necessarily a much slower procedure and hence a serious disadvantage.
Only one known essentially solid state electrosurgical system, the "RELIANCE Brand Model ES-47 Electrosurgery System", provides both cut and fulguration currents. However, such system necessarily provides these two currents to separate active electrodes and thereby suffers from the disadvantage that the surgeon must expend extra time in switching active electrodes when sequentially cutting and fulgurating.